Field of the Invention
The invention relates to a flowmeter, in particular for use in custody transfer, having a housing, at least one evaluation unit arranged in the housing and having an interface arranged in the housing for communication with an external control unit, wherein the evaluation unit can be written with data via the interface.
Description of Related Art
Flowmeters of the above type are known from the prior art in various designs. Special conditions are required in flowmeters for use in custody transfer, in particular because fair trade needs to be ensured or because measuring accuracy is a benefit to the public, often due to a quantity-based tax being raised on the transported and extracted medium.
Custody transfer occurs when the possession of a fluid, such as oil, gas, water, or steam, changes hands from one owner to another. The owner could be, for example, an oil or gas production company, a pipeline company, or a utility company. What typically happens in a custody-transfer flow measurement situation is that one or two custody-transfer flowmeters measure the volume or mass of fluid before the transfer is made, and then another set of flowmeters measures the flow after the transfer. What makes custody transfer unique among flowmeter applications is that money changes hands and that accuracy requirements are higher than they are for most other applications.
Custody transfer flow measurements are subject to a plurality of legal and institutional regulations, through which a particular certainty of the measurements is ensured. For example, regulations of the International Organization of Legal Metrology (Organisation Internationale de Métrologie Lègale (OIML)), here, for example, the OIML Certificate R 117 for measuring systems of liquids other than water. Recommendations of the OIML are often incorporated into national standards and, thus, are held in regard world-wide. A European guideline addressing the requirements for authorizing a measuring device for use in custody transfer is the guideline 2004/22/EG of the European Union.
A central characteristic of flowmeters for use in custody transfer is its tamper protection. It should be ruled out with great probability, that a flowmeter for use in custody transfer can be tampered with from outside in such a manner that its measuring accuracy is no longer ensured or, respectively, that the measurement is falsified. This could take place in that, for example, calibration parameters set by an official inspection authority and stored in the flowmeter are overwritten. Such a tampering is by all means to be prevented in the respect that a tampering with technical means is made more complicated and that successful tampering is clearly recognizable.
It is known that the opening of flowmeters or the housings of these flowmeters is prevented using a seal, so that influencing the flowmeter is made possible first when the seal is broken and, thus, is detectable. Modern flowmeters can often no longer be easily opened, for example, due to provided explosion protection measures.